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DS-SIG40 R1.8

Figure 4.3 - Writing to a Control Register

In order to read from a control register, the host sends one byte. The byte should be sent more than

200nSec after lowering HDC. The byte begins with the address of the register followed by ”D”H. The

SIG40 will then output the content of the register to pin HDO.

Read Command

Register Address[3:0]

D(hex)

Read Command

Figure 4.4 shows the pins involved in the reading process:

Figure 4.4 - Reading from a Control register

Note: Writing to Register 1

Writing a change frequencies command to register 1 is not always interpreted correctly by the device.

The device will switch to the correct frequencies pair however, it will not function properly, resulting a

communication lost.

Workaround: When changing frequencies by writing to register 1, use the following procedure:

Lower the H_DC.

Send a command to register 1 containing the require frequencies pair and a false bit rate.

Raise the H_DC

Lower the H_DC

Send a command to register 1 containing the require frequencies pair and the required bit rate.

Raise the H_DC.

For example, when wanting to work with frequencies 3.58MHz and 4.5MHz at 19.2Kbps the correct way

to program the device is described in Figure 4.4.1

0x15C0

0x15F0

HDI

HDC

Sending a command

for 3.58MHz/4.5MHz at

38.4Kbps

Sending a command

for 3.58MHz/4.5MHz at

19.2Kbps

Figure 4.4.1 – Writing to Register

Note: Changing only the bit rate can be done with a single write, as described above.

4.4

Loopback

The device operates like a transceiver, therefor while transmitting or writing a command the HDI signal

is looped back to the HDO pin.

start bit

Address

stop bit

HDI Read

Command:

HDC:

0

1

3

2

HDI

HDC

stop

bit

start

bit

Address

start

bit

stop

bit

Configuration Data

0

1

3

2

0

1

3

2

4

5

7

6

d

a

t

a

start

bit

Data